Ensuring patient safety remains a critical issue for health care systems. In particular, ambulatory (outpatient) health care settings are vulnerable to patient safety concerns. The majority of health care is delivered in ambulatory settings, with 1.2 billion outpatient visits annually in the United States (U.S.). Between failures of monitoring, and missed and delayed diagnosis, there is significant morbidity and mortality from patient safety problems in outpatient care. Although strides have been made in recognizing and preventing adverse events, little is known about the epidemiology of patient safety in ambulatory care settings and factors that contribute to these disparities. The overall goals of this proposal are t examine the epidemiology of patient safety in ambulatory care settings that care for diverse, low-income populations as follows; (1) to characterize the incidence and prevalence of specific safety gaps, by race/ ethnicity and language proficiency; (2) to gather in- depth, qualitative evidence about strategies that can improve safety and characterize disparities in patient safety; (3) to pilot-test patient safety monitoring methodologies in a diverse sample of five safety net health care systems; and (4) to develop a measurement and error investigation toolkit for dissemination amongst safety-net health care systems. Specifically, we will identify the extent of missed notification for actionable test results and extent of missed monitoring for high-risk populations. These two process gaps, periodic monitoring of high-risk conditions and notification of actionable abnormal test results, both lead to preventable patient harm. While these care gaps are documented, the extent of disparities in harm and the populations at highest risk remain unclear. To further deepen this knowledge, we will elucidate underlying causes for these safety gaps, focusing on disparities we identify in the data. Finally, we aim to give safety-net health systems participating in this study the methodological tools to conduct measurement of these safety gaps and perform event investigation, in order to set the stage for future improvement and innovation work to close gaps in disparities. We propose a collaborative Safety Promotion Action Research and Knowledge Network (SPARK Network) to achieve the following specific aims: 1) to develop feasible, timely, and accurate electronic measures of patient safety notification and monitoring gaps in an ambulatory care setting for high-risk sub- populations and characterize the extent of disparities in patient safety; 2) to conduct a root cause analysis of patient safety notification/ monitoring gaps in five public ambulatory care settings to identify factors contributing to these disparities; and 3) to evaluate the pilot implementation of patient safety monitoring methodologies developed from Aims 1 and 2 across five diverse ambulatory health care settings. We envision that pilot findings from this project wil result in a measurement and root cause analysis toolkit of patient safety monitoring methodologies that can be widely disseminated across health care systems that care for diverse populations.